The field of the invention generally relates to microfluidic structures and methods of using them to interface measurement devices to living cells. More specifically the field of the invention relates to the creation and control of chemical gradients over length scales commensurate with the size of biological cells.
Much of modern biological research is concerned with the study of living cells. Countless investigations of cells have greatly increased our understanding of biological processes and have led to improved treatment of disease and reduced suffering of ill patients.
Many biological advances come from the application of known research techniques to cells or biological molecules which have not been studied before. However, the greatest leaps in understanding often occur when new research tools are invented. Nearly 400 years ago, for example, Anton van Leeuwenhoek of Holland pioneered the use of microscopes in biology. He was the first to see and describe bacteria, yeast plants, the teeming life in a drop of water, and the circulation of blood corpuscles in capillaries.
Today researchers not only look at cells, but probe, excite, influence and control them with a variety of methods, always with the goal of understanding more about how cells work and interact with their environment. Often glass capillary tubes, drawn out to have very sharp tips, are used to probe cell behavior and modify a cell's local environment.
Conventional research techniques include using tubular glass micropipettes with tips as small as one micron in diameter. Researchers use micromanipulators to position micropipette tips near cells under a microscope. For “patch clamping” experiments a tip is sealed over a patch of the cell membrane. For experiments on “chemotaxis”, or the movement of cells along gradients of concentration of dissolved substances, a tip is placed very close to the cell and a solution is squirted out.
Micropipettes are used in many other types of biological experiment, but fundamentally the tip of the pipette is always brought very close to, or in contact with, a cell for the purpose of modifying or sampling the cell's local environment. A solution may be squirted out near the cell in an attempt to provoke a reaction from it. Alternatively a small volume of solution from the cell's immediate surroundings may be sucked into the end of the pipette for analysis.
One of the limitations of micropipettes is that they are difficult to manipulate due to their large size in relation to the cell being measured. A highly trained technician is required to use them effectively. It is also generally not feasible to operate more than one micropipette at a time during an experiment. Therefore only single cells, rather than organized collections of cells are studied.
According to Klemic et al. in Biosensors and Bioelectronics (v. 17, p. 597, 2002) “there is tremendous interest in improving the throughput and ‘ease of use’ of the patch clamp method, primarily to facilitate drug screening in the pharmaceutical industry . . . ” Further, the conventional “method is not practical for high-throughput screening because it requires a skilled operator to manually manipulate the glass pipette onto the cell.”
Micropipettes are used in chemotaxis experiments to show how cells may be attracted to concentration gradients of certain substances dissolved in solution. Using microscopes, researchers have made movies of cells chasing a micropipette tip whenever a solution is ejected from the tip. It would be highly desirable, however, to be able to characterize and quantify the concentration gradient that influences the cell or even to create a concentration gradient around a cell that is fixed in position.
Overall, a better interface to living cells is needed. A long-felt need for a cell interface exists in the art of cell studies as evidenced by the popularity of micropipettes in the face of their limited capabilities.
Structures that could create controllable, highly localized concentration gradients in the immediate vicinity of cells would be useful in myriad biological experiments. Structures that could organize cells into ordered groups would be advantageous for parallelizing cell investigations instead of performing experiments one cell at a time. Structures that could deliver reagents to the immediate vicinity of cells would be useful for drug screening. The present lack of structures with these capabilities would make the invention of a new cell interface device all the more surprising.